Definitions for the strength of evidence (Design/Class 1-3) and strength of recommendations (Level A-C) are provided at the end of the Major Recommendations.
- Can lower extremity deep venous thrombosis (DVT) be excluded by a negative D-dimer?
Level A recommendations. None specified.
Level B recommendations. In patients with low clinical probability for lower-extremity DVT, the following test results can be used to exclude DVT:
- A negative quantitative D-dimer assay result (turbidimetric or enzyme-linked immunosorbent assay [ELISA]) for exclusion of proximal (DVT from the knee to the inguinal ligament) and distal (DVT isolated to the calf) lower-extremity DVT.
- A negative whole blood D-dimer assay result in conjunction with the Wells et al scoring system for exclusion of proximal and distal DVT.
- A negative whole blood D-dimer assay result for exclusion of proximal lower-extremity DVT.
Patients with a moderate-to-high risk of lower-extremity DVT cannot have DVT excluded by a single negative D-dimer test.
Level C recommendations. None specified.
- Can lower-extremity DVT be excluded by normal findings on a venous ultrasonographic scan?
Level A recommendations. None specified.
Level B recommendations. In patients with low clinical probability for lower-extremity DVT, negative findings on a single venous ultrasonographic scan in symptomatic patients excludes proximal (DVT from the knee to the inguinal ligament) lower-extremity DVT and clinically significant distal (DVT isolated to calf) lower-extremity DVT. In patients with moderate to high pretest probability of lower-extremity DVT, serial ultrasonographic
examinations need to be performed. (Serial venous ultrasonographic examinations refers to scheduling a patient for follow-up ultrasonographic examination within 5 to 7 days or referral of the patient to a primary care physician for follow-up management). Patients with high suspicion of pelvic or inferior vena cava thrombosis may require additional imaging technique.
Level C recommendations. None specified.
- What are the indications for fibrinolytic therapy in lower-extremity DVT?
Level A recommendations. None specified.
Level B recommendations. None specified.
Level C recommendations. Consider fibrinolytic therapy
in patients with limb-threatening thrombosis of the iliofemoral system in whom the benefits of treatment outweigh the risks of serious bleeding complications.
Definitions:
Strength of Evidence
Literature Classification Schema*
Design/Class 1
- Therapy#: Randomized, controlled trials or meta-analyses of randomized controlled trials
- Diagnosis&: Prospective cohort using a criterion standard
- Prognosis**: Population prospective cohort
Design/Class 2
- Therapy#: Nonrandomized trial
- Diagnosis&: Retrospective observational
- Prognosis**: Retrospective cohort, case control
Design/Class 3
- Therapy#: Case series, case report, other (e.g., consensus, review)
- Diagnosis&: Case series, case report, other (e.g., consensus, review)
- Prognosis**: Case series, case report, other (e.g., consensus, review)
*Some designs (e.g., surveys) will not fit this schema and should be assessed individually.
#Objective is to measure therapeutic efficacy comparing >2 interventions.
&Objective is to determine the sensitivity and specificity of diagnostic tests.
**Objective is to predict outcome including mortality and morbidity.
Strength of Recommendations
Level A recommendations. Generally accepted principles for patient management that reflect a high degree of clinical certainty (i.e., based on "strength of evidence class I" or overwhelming evidence from "strength of evidence class II" studies that directly address all the issues).
Level B recommendations. Recommendations for patient management that may identify a particular strategy or range of management strategies that reflect moderate clinical certainty (i.e., based on "strength of evidence class II" studies that directly address the issue, decision analysis that directly addresses the issue, or strong consensus of "strength of evidence class III" studies).
Level C recommendations. Other strategies for patient management based on preliminary, inconclusive, or conflicting evidence or, in the absence of any published literature, based on panel consensus.
There are certain circumstances in which the recommendations stemming from a body of evidence should not be rated as highly as the individual studies on which they are based. Factors such as heterogeneity of results, uncertainty about effect magnitude and consequences, strength of prior beliefs, and publication bias, among others, might lead to such a downgrading of recommendations.